It has long been known and practiced in agriculture that certain biological (i.e. microbial) inoculants can be used with certain selected crop species to facilitate the growth of crop plants of that species or to assist the crops of that species in resistance to particular pathogenic organisms. In addition, there is current research data suggesting that there may be several species of root-colonizing microorganisms which may be useful in promoting the growth of flowering plants or acting as antagonists to disease organisms, and thus acting to improve the yield of crop plants. Schroth and Hancock, "Disease-Suppressing Soil and Root-Colonizing Bacteria,"Science, Vol. 216, pp. 1376-1381 (1982). The most long established use of microbial inoculants is the quite common practice of inoculating soybeans and other legumes at planting with bacterial cultures of the genus Rhizobium, so that the Rhizobium bacteria will form colonies in nodules within the roots of the soybean or other legume in which they will fix nitrogen symbiotically for the benefit of the plant as well as the bacteria. Currently this inoculation can be done by several techniques, none of which is optimal for all purposes. Techniques used in current practice include coating the seeds, dusting planted seeds or crops, or by spreading moist living inoculant in the furrows of planted seeds.
There has been a significant effort in the past to optimize products for preparing bacterial crop inoculants, focused particularly on Rhizobium inoculants. The typical process for preparing such inoculants usually requires both a fermentation process to grow up sufficient quantities of bacteria, and a stabilization or formulation process to either stabilize the mature bacteria for storage and shipment in an inactive state or to formulate the bacteria in an active culture for direct delivery to the field. Typically in the prior art the fermentation and formulation processes have been considered quite distinct, and one or more handling or processing operations are required to successfully transfer viable bacteria from fermentation to the formulation process. In addition, in prior art processes the usual carrier for viable Rhizobium cultures was peat. Since direct cultivation of bacteria on peat has not been commonly considered practical, because of microbial contaminants in peat, because peat is difficult to sterilize, and because toxic substances can be created in peat during sterilization, when a peat carrier has been used, a clear separation of the fermentation process from the formulation process was usually required.
It has also been recognized by some in the agricultural field that other, non-Rhizobium microbial organisms can foster the growth of common crop plants. For example, it has been known in the prior art that many fungi are found in association with the roots of certain specific vascular or woody plants. The type of association between fungi and plants is not well characterized and there is not a clear understanding or agreement among mycologists as to which of these associations are more properly characterized as symbiotic and which are more properly termed pathogenic. The association produced by a fungus with the roots of a plant is often referred to as a mycorrhizal association, although there is a poor understanding of this association.
It has now been reported specifically that some certain fungal species or strains have the capability to be antagonists for certain other plant pathogens. For example, it has been reported that the fungus Talaromyces flavus has the capability to be an antagonist for the fungal pathogen Verticillium dahliae in the cultivation of eggplant. Marois, et al., "Biological Control of Verticillium Wilt of Eggplant Solanum-Melongena in the Field", Plant Disease, 66:12, pages 1166-1168 (1982). Other fungal species have been reported to have similar effects. Papivizas, "Survival of Trichoderma-Harzianum in Soil and Pisum-Sativum Cultivar Perfectid-Freezer and Bean Phaseolus-Vulgaras Cultivar Blue-Lake", Phytopathology, 72:1, pages 122-125 (1982). In U.S. Pat. No. 4,259,317, a preparation for the protection of emerging sugar beets against damping-off, which is caused by a parasitic fungus, is disclosed which includes the use of the fungus Pythium oligandrum, which is used as an inoculant on the sugar beet seed to prevent damage to the plant by other fungal species.
One difficulty in using fungi as crop inoculants is the difficulty in propagating and producing large quantities of propagatable fungal material. The state of the art in fungal cultivation is not far advanced. For a fungal species to be useful as a crop inoculant, it must be producible in reasonable quantities and the end product of the production process must be reasonably easily handled and have a sufficiently long shelf life to be commercially useful. While it is possible for suitable microbial inoculants to be maintained in a living moist state, moist cultures present problems of transportation and storage. It is therefore obviously preferable if the fungi can be reduced to a dried or powdered state which is nevertheless viable upon planting in agricultural soils.
At least one prior attempt is known to devise a method for producing and preparing fungal agents for use as agricultural inoculants. That method is disclosed in U.S. Pat. No. 4,530,834 to Soper and McCabe, assigned to the United States Department of Agriculture. That method includes culturing the mycelia of a fungal agent in a suitable media and then harvesting the mycelia on a mesh screen to make mycelial mats. The mycelial mats are then treated with a protective agent, which is preferably a sugar solution, until they are saturated. The mycelia are then incubated and air dried at ambient room temperatures. The present invention is intended to be a more convenient methodology for creating a similar dried propogatable fungal product.